[AVX-512] Add test case to check shuffle decoding for masked vpermilps for r284450.
[AVX-512] Add test case to check shuffle decoding for masked vpermilps for r284450.

This is harder to do for vpermilpd as shuffle combining turns the constant vector into an immediate since all vpermilpd's inputs with constant vector can also be encoded with the immediate form.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@284455 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm